This invention relates to semiconductor devices in general and, in particular, to those especially well adapted for use in the electronic driver circuits of electric motors, among other applications. More particularly, the invention pertains to an integrated semiconductor device incorporating transistors or like active elements, featuring provisions for inhibiting or restricting the action of parasitic transistors under certain foreseeable conditions in use of the semiconductor device in motor drive systems or the like.
Japanese Unexamined Patent Publication No. 63-18660 is hereby cited as teaching a motor drive system (FIG. 1) representing a typical application of the instant invention. The motor drive system has a required number of motor driver circuits of like construction coupled one to each of the motor coils in star connection. Each motor driver circuit has four transistors in addition to two diodes. When the motor driver circuits were fabricated in the form of an integrated semiconductor circuit (FIG. 2), a parasitic transistor was unavoidably created between two neighboring ones of the transistors of each motor driver circuit. The parasitic transistor conducted when the output of the driver circuit had a negative potential, preventing the motor drive system from driving the motor exactly as required.
In order to prevent the appearance of the parasitic transistor, the cited Japanese patent application suggests the creation of a floating region between the two transistors in question which are formed island-like in the semiconductor substrate and which are separated therefrom via pn junctions. The floating region was intended to accomplish its purpose by making the space between the transistors higher in resistance. An objection to this prior art device is its inordinate space requirement between the transistors, adding substantively to the size of the semiconductor device.